Carburetor for internal combustion engines

ABSTRACT

A carburetor for internal combustion engines of the type including the idling system, provides guide passage means for conducting the flow of fuel, which tends to adhere in the state of liquid upon the inner wall surface of the throttle bore in idling or low-load operations of the associated engine, down onto the bottom area of the throttle valve, so that the whole of liquid fuel be thoroughly atomized before leaving the carburetor.

United States Patent 11 1 Matsumoto 1 1 Feb. 18, 1975 [54] CARBURETORFOR INTERNAL 1,625,572 4/1927 Simpson 261/DI G. 21

N 1,785,501 12/1930 Secor 261/DIG, 55 COMBUSTION ENGI ES 2,328,7369/1943 7 Mock 1 261/65 [75] Inventor: Hiromitsu Matsumot sh zu ka,3,393,984 7/1968 Wisman 261/65 V I Japan 3,414,242 12/1968 Bonteleux261/41 D [73] AssigneeszYamaha Hatsudoki Kabushiki FOREIGN PATENTS ORAPPLICATIONS I Kaisha, lwatatshiluokatlapan 1,233,027 5/1960 France261/65 221 Filed: Nov. 20, 1973 Primary ExaminerT1m R. Mlles 1 1 pp b 1Attorney, Agent, or Firm-POll0Ck, Philpitt & Vande Sande [30] ForeignApplication Priority Data v Nov. 24, 1972 Japan 47-134551 ABSTRACT Acarburetor for internal combustion engines of the [52] US. Cl 261/41 D,26l/DIG. 55 261/65 type including the idling System provides guide [51]Int. Cl. FOZm 19/06 Sage means conducting fl f f l which [58] F'eld of261/DIG- 55, 41 D, tends to adhere in the state of liquid upon the inner261/65 wall surface of the throttle bore in idling or low-load Ioperations of the associated engine, down onto the [56] References C'tedbottom area of the throttle valve, so that the whole of UNITED STATESPATENTS liquid fuel be thoroughly atomized before leaving the 1,580,6344/1926 Ball .Q 261/DIG. 55 u or.

22 Claims, 15 Drawing Figures I 1 'CARBURETOR FOR INTERNAL COMBUSTIONENGINES BACKGROUND OF THE INVENTION The present-invention relates to acarburetor for internal combustion engines, and more particularly to animproved carburetor which has excellent characteristics of carburetionin terms of complete atomization of the fuel attainable in starting,'idling or low-load operation of the engine. j

Generally, the low-speed fueling or idling system incorporated in theprior art carburetor includes an idle port and by-pass ports incommunication with the float chamber via a pilot jet, those ports beingopened in the throttle bore or induction pipe adjacent the throttlevalve. When the throttle valve .is closed or slightly opened for idling,starting or low-load running of the engine, the fuel with breeding airis discharged in'the induction pipe through the idle port or by-passports. With such ordinary arrangement of idling system, however thedifficulties have occurred in that the action of the breeding air onlyis not enough to effect full atomization or vaporization of the liquidfuel as desired, so that a large portion of the fuel adheres or driftsaround the inner wall surface of the induction pipe, still in the stateof liquid, and is forcedv into the associated combustion chambers in theengine. Because of this significant supply of not-atomized fuel into thecombustion chambers, it was necessary to provide an additional orexcessive supply of fuel so as to secure an adequate airfuel ratio. Thisnaturally caused vexious problems eg of the engine operation in idlingand excessive fuel consumption. Further, anotherproblem has been raisedin that since the liquid fuel travels along the inner wall surface ofthe carburetors induction pipe and the intake manifold of the engine,the combustion chambers are supplied with the liquid fuel in pulsatorymotion thereby causing instabilities of the engine revolution. Stillanother problem has been that in the case of a single carburetor forfuel distribution to a number of combustion chambers, the ratioof fueldistribution shows unevenness as one of the combustion chambers nearestthe carburetor tends to be excessively supplied with the fuel, hencecausing objectionable vibrations or unsteady running of the engine.Still further, there has been involved the difficulty that since thefuel takes rather a lengthy period of time to reach the associatedcombustion chambers, the working response of the engine is deteriorated.Y

SUMMARY OF THE INVENTION 5 This invention, therefore, is directedtoeliminate the above prior art drawbacks by providing a carburetor forinternal combustion engines of the type comprising an induction pipehorizontally arranged downstream of the Venturi portion, abutterfly-type throttle valve, and an idle port on the upper wall of theinduction pipe being opened in the induction pipe adjacent the positionassumed by the topperipheral edge of the throttle valve when the valveis closed or slightly opened, chara'cterized by the provision of passagemeans formed wall surface of the induction pipe in the downstreamdirection and conduct said flow of fuel downwardlyand further passagemeans formed around the journal portions of the valve shaft, saidfurther passage means functioning to conduct said fuel flow, which hasreached above the valve shaft, to the lower central surface area of thethrottle'valve' while turning the-flow the state of liquid along theinner wall surface of the induction pipe toward the combustion chambersof the engine, is all captured by the passage means and caused to flowdownwardly circumferentially along said passage means under theinfluence of its self-weight or suctionforce produced in the inductionpipe, tobe-gathered around the central surface area of the throttlevalve through said further passage means. The liquid breeding throughthe idle port or by-pass ports. To-

gether with this twofold effect of fuel atomization the arrangement ofthe invention warrants that all the volume of fuel discharged from theports as not-atomized or in the state of liquid be completely atomizedthrough the lower valve gap before leaving the induction pipe of thecarburetor, whereby avoiding the prior art problems of inadvantageouslysupplying some amount of liquid fuel into the associated enginecylinders. Hence, the inventionis in effect advantageous in that becauseof no liquid fuel being takenin the engine cylinders it is possible toset the desired air-fuel ratio with a fuel mixture far leaner than thatin the prior art carburetor which has needed an excessive supply offuel, thereby deterimental substances such as I-IC, CO, etc. involved inthe exhaust gas are significantly reduced in quantity. Further, theinvention has advantages of reduction in fuel consumption, stabilitiesin the engine operation,

and improvements on the response characteristic of the around the innersurface of the induction pipe, said passage means functioning to preventfuel discharged though the idle port from flowing along the upper innerengine as well as its starting characteristic-under cold conditions. p

BRIEF DESCRIPTION OF THE DRAWINGS- invention;

FIG. 8 is an enlarged section of the same arrangement however accordingto a fourth embodiment of the invention;

FIG. 9 is also an enlarged section of the same arrangement still howeveraccording to a fifth embodiment of the invention;

FIG. is a perspective view of the valve and shaft assembly according tothe fifth embodiment of the invention;

FIG. 11 is an enlarged section of the arrangement around the valveaccording to a sixth embodiment of the invention; FIG. 12 is a sectiontaken along the line XII XII of FIG. 11;

FIG. 13 is a section taken along the line of FIG. 11 I FIG. 14 is asection taken along the line XIV XIV of FIG. 11; and

FIG. is a perspective view of the valve and shaft assembly according tothe sixth embodiment of the invention.

DESCRIPTION OFTI-IE PRESENTLY PREFERRED EMBODIMENT FIGS. 1, 2, 3 and 4show a carburetor and its portion incorporating the first embodiment ofthe invention.

In FIG. 1, the carburetor l principally includes: a substantiallyhorizontally extending air intake pipe 2; a

XIII XIII piston valve 5 for varying the sectional area of the Venturiportion 4 in response to negative pressure produced in the inductionpipe 3 by the manifold suction of the associated engine (not shown) afloat chamber 6 for fuel storage with a constant fuel level; and athrottle valve 7 which is operatively connected to the accelerator pedal(not shown) for rotation to vary the valve opening in the induction pipe3.

The piston valve 5 is slidably supported in a piston valve cylinder 8which is integrally formed withthe intake pipe 2. The piston valve 5 isprovided at the top with a diaphragm 9 secured in air-tight manner,forming a suction chamber 10 with a casing 11. A coil spring 12 isanchored on the casing 11 so as to urge the piston valve 5 in thedownward direction. The bottom of the piston valve 5 provides a surfaceportion 14 being tapered downwardly as viewed from the air intake side13, a horizontal surface portion 15, an orifice 16 through which air inthe suction chamber 10 is drawn out by negative pressure produced in theVenturi portion 4, and a jet needle 18 which is adapted to be thrusteddeep in a coworking needle jet 17.

The float chamber 6 is formed by the lower wall of the air intake pipe 2and a float chamber casing 19. The float chamber 6 stores in it a volumeof fuel with a constant fuel level 22 attained by means of a needlevalve and a float 21. A supporting block 23 having a port opened in thechamber is provided integral with the float chamber case 19, supportinga main jet 24 and the needle jet 17 in alignment with the piston valve5. The needle jet 17 is opened in the Venturi portion 4 in the intakepipe 2. Further, the supporting block 23 supports a pilot jet 26 in apassage 37 branched from above the main jet 24.'The pilot jet 26-has anopening 27 which is in communicationvia a passage 29 with an air jet 28opened around the outer periphery of the air intake 13.

The pilot jet 26 is further communicated with an idle port 31 and bypassports 33 through a passage 30 extending across the induction pipe 3. Theidle port 31 is opened on the inner upper wall surface of the inductionpipe 3, in the vertical direction, and more specifically it is locatedslightly downstream of the position of the upper edge of the throttlevalve 7 that is to be assumed when the valve 7, which is secured on avalve shaft 33 by screws 34, is closed. The by-pass ports 32 are openedupstream of the idle port. Above the idle port, there is provided anadjustable screw 35 for control of air-fuel flow through the idle port31.

Around the inner wall surface of the upper half section of the inductionpipe 3, there is essentially provided a semicircumferentially extendingpassage means 36 in the form of a groove having a substantially U-shaped section opened in the induction pipe, which groove extending fromadjacent one journal portion 33A, facing downstream, of the valve shaft33 toadja cent the other journal portion 33A, facing downstream, of theshaft, in the assumed position of the valve being closed, after passingdownstream the idle port 31. The journal portions 33A of the valve shaft33 are of circular section, and the intermediate portion 338 of theshaft exposed in the induction pipe 3 is flattened by reducing thethickness by one-fifth to one-fourth of the diameter of the journalportion so as to constitute two parallel plane surfaces 39A, 39Bsymmetrical with each other in respect of the shaft axis. While thesurface 39A facing upstream extends fully across the bore of theinduction pipe 3, the surface 398 is bounded at each lateral end byfurther passage means in the form of an inclined step surface 40 whichextends with an angle of in respect to the shaft axis starting fromslightly outside the respective lower end of the above describedsemicircumferential groove 36 while terminating at the inner locationabout one-sixth of the induction pipe diameter apart from the pipe wall.This step surface 40 is substantially vertical with respect to thesurface 398. Both. of the two convergent passage means 40 thusconstitute extensions of the above described semicircumferential groove36. Between the two plane surfaces 39A, 39B, is formed a slot 41intowhich the throttle valve 7 is inserted and secured by fasteningscrews 34. The throttle valve 7 is in operative association with theaccelerator means (not shown) through the valve shaft 33. With theaccelerator means set for idling, the throttle valve 7 is closed withminor gaps 42 provided on the upper and lower ends of the valve. j 7

According to the carburetor 1 arranged above, the

idling system will be operated as follows.

. Due to the generation of suction or negative pressure in the inductionpipe caused from the suction force by the engine cylinder, air flows inthrough the upper and fuel which has not been atomized is conducted bythe air stream through the valve clearances 42 to spread out upon theinner wall surface of the induction pipe 3 from the idle port 31 andby-pass ports 32, and is drawn downstream in the liquid form adheringupon the inner wall surface of the pipe 3. When this liquid fuel reachesthe passage means or semicircumferential groove 36, it is prevented fromflowing further downstream, and is conducted downwardly along the groove36. Two descendent flows of that fuel is then conducted by therespective passage means or inclined step surfaces 40 formed on thevalve shaft 33 to change their flow directions so that they tend toconverge around the center area of the downstream surface of thethrottle valve 7. Subsequently, the flows of liquid fuel reach thebottom of the valve 7, where the fuel is subjected to a highspeed streamof air through the valve clearance 42 so that the fuel is completelyatomized and drawn downstream in the pipe 3 toward the associatedengine.

It is to be noted that since the inner or lower end of each passagemeans 40 is located with a distance L from theinner wall of theinduction pipe 3, the fuel will never attach on the inner surface oftheinduction pipe 3 while falling-along the surface of the throttle valve7. Also, it is to be noted that although the convergent passage means 40have been described as inclined by 45, this inclination mayalternatively be from to 60C, depending on the applicationcircumstances. However, the range from to 65 has generally proved mostdesirable in terms of compatibly securing a smooth flow of fuel on theinclined step surface and prevention of the fuel being drifted to theinner wall surface of the pipe 3.

FIGS. 5 and 6 show the second embodiment of the invention, wherein onlythe arrangement around the induction pipe is shown as other parts orportions are the same as described with reference to the firstembodiment.

The semicircumferentially extending passage means 36A provided aroundthe inner wall surface of the induction pipe 3 is in the form of agroove having a U- shaped section extending from above one journalportion of the valve shaft 33 to above the other journal portion of theshaft 33. Howver, this groove is shaped such that for the upper halflength of the groove, the sidewall 136A on the upstream side shows agradual increase of angle relative to the inner surface of the inductionpipe 3, as shown, from the top toward the middle of the groove length,in a manner that the side wall 136A forms-a curved surface havinggradually changing slopes relative to the bottom, while the side wall1368 on the downstream side and the side wall 136A extending over thelower half length of the groove are substantially perpendicular to theinner surface of the pipe 3. The valve shaft in this embodiment isuniformly of circular section, securing the throttle valve 7 insertedinto a slot formed longitudinally, centrally of the shaft by means offastening screws 34. The valve shaft 33 is provided at each journalportion with passage means 64in the form of an inclined through-holestarting from the juncture between the downstream surface of thethrottle valve and the upper portion of the shaft journal, toward thelower center ofthe valve, through the shaft. In the valve closedposition, the upper opening 65 of each through-hole 64 is adapted to belocated for substantially continuous communication with the respectivelower end of the passage means 36A, and each through-hole 64 extendsover both axial sides of the junction 66 between the valve shaft and theinner surface of the induction pipe 3. The inclination of each passage64 is'set at around 45 in angle with respect to the shaft axis. 3 I

With this arrangement of the second embodiment, almost the same effectcan be obtained in conducting the flow of liquid fluid along the twopassage means, for full atomization through the bottom clearance 42, asthat described with reference to the first embodiment. Additionally,however, it will be assured that thanks to such gradual changes in thesectional shape of the groove, there occurs a flow of air directeddownward in and along the passage 36A so that the downward movement ofthe liquid fuel therealong be far more facilitated. This will results inthe provision ofa better response character of the associated engine.

In the third embodiment of FIG. 7, there is provided passage means' inthe form of substantially semicylindrical conducting member 36B which isfittingly inserted in the induction pipe 3 and secured by a bolt 136C.The conducting member 368 has its upstream edge which extendssemicircumferentially between both journal portion areas of the valveshaft and forms a surface 136D substantially perpendicular to the innersurface of the induction pipe 3. Also, there is provided further passagemeans on the valve and shaft assembly in the form of a valve supportingmember 50 having a trapezoid section. ltsbevel side surfaces form minorangles with the downstream surface of the valve 7. With thisarrangement, the flow of liquid fuel is guided downwardly along and bythe surface 136D of the passage means 363 also with the additional aidof an air flow occurring therealong in the downward direction, and thenthe liquid fuel is further conducted toward the bottom of the valvethough the surface 40 and the bevel side surface 50A of the supportingmember 50. Thus,

a very smooth and rapid flow of liquid fuel is secured in theoverall'length of conducting passage.

FIG. '8 shows the fourth embodiment of the invention, which is the sameas the third embodiment except ing the sectional configuration of theupstream edge of the passage means. As shown, the semi-cylindricalpassage means 36C has the upstream edge of trough-like section opened tothe upstream with the inner extreme end 136F projecting a little moreupstream than the outer extreme end 136E. This arrangement securesreliable conduction of the fuel flow in a desired and positive manner aswell as a quick flow of the liquid fuel by the aid of an air streameasily occurring along the passage means.

FlGS. 9 and 10 show the fifth embodiment which is the same as theprevious embodiments of FIGS. 1 through 4 excepting passage meansprovided on the throttle valve, valve shaft and inner wall of the induc--tion pipe. As shown, passage means 36D consists of a groove 51according to the first embodiment and a semi-cylindrical member 52similar to the member 368 of the third embodiment. In FIG. 10, the valveshaft 53 having journal portions 53A of circular section provides theintermediate portions 533 adapted to be exposed in the induction pipe 3.This intermediate portion 53B is reduced in thickness from thedownstream side 'so as to be of crescent shape in section, and thethrottle valve 7A is secured on the surface 538 by screws 34. Around thejuncture between the valve 7A and the innerend of each journal portion53A, the valve shaft provides a cut-out portion 54 of plane surfaceperpendicular to the surface of the valve 7A and inclined by 45 withrespect to the axis of the shaft 53.

It is of course arranged that in idling or when the valve 7A is slightlyopened, each cut-out portion 54 is positioned in continuation with therespective lower end of the above described passage means 36D. Also, the

valve 7A is provided with a couple of passage means 55 each in the formof a substantially triangular plate member which has a thicknesscorresponding to that of the valve and a main side surface 56 beinginclined 45 with respect to the shaft axis. The upper end of the surface56 is formed in continuation with the respective cut-out portion 54. Thelower end 57 of the surface 56, or plate member 55 terminates with adistance of about one-fourth of the vertical center height of the valveapart from the bottom of the valve. In like manner, with thisarrangement, there can advantageously be secured a quick flow of airdirected downward along the groove 51 due to differential air pressurebetween the top and bottom groove zones, thereby downward conducting of.the liquid fuel therealong being facilitated. The cut-out portions 54and the surfaces 56 of the plate member 55 serve to guide the flow ofliquid fuel to be delivered onto the surface of the valve 7A in a widelydispersed pattern, as best shown in FIG. 10. Thus, the liquid fuelundergoes a significantly wide range of atomization at the valve gap 42.

FIGS. v11, 12, 13, 14 and show the sixth embodiment of the invention.

Here, passage means 36E is constituted with a groove 58 formed aroundthe inner wall surface of the induction pipe 3 and a further groove 59.formed at the upstream edge of a semi-cylindrical member 136G so thatsubstantially tubular passage means be provided. As best shown in FIGS.12 through 14, the grooves 58 and 59 show the same radius in section iftaken along the same section, but these radii are reduced graduallytoward the lower end of the tubular passage so that atop the passage,the tubular inner space 36E be maximum opened, in the upstreamdirection, with the projection edge 60 of the member 1366 spaced mostapart from the groove 58, while the inner space 365 is closed with theprojection 60 beingin contact with the inner wall surface of theinduction pipe 3, at the level one-fourth of the passage length apartfrom the bottom. As seen in FIG. 15, the valve shaft 61 with journalportions 61A and the intermediate portion 618 similar to the fifthembodiment, is provided with step surfaces 62, 62 each with 45inclination, perpendicular to the upstream surface of the valve 7similarly secured on the intermediate portion 61B by screws 34. Theupper end of each step surface 62 is located within the journal portion61A, extending beyond the lower end of the respective passage means 36E.

This arrangement achieves the same effect as with the fifth embodimenthowever with a more effective advantage of using the action of airstream through the lower half length of closed'passage. Similarly to theprevious embodiments, there can advantageously be provided a very quickflow of liquid fuel all the way along the passage 36E and surfaces 62formed on the valve shaft 61 and wide dispersion of the liquid fuel uponthe surface of the valve so as to be fully atomized at the lower gap. Nodrifting of the liquid fuel off the valve surface or onto the innersurface of the induction pipe will occur.

I claim:

1. A carburetor for internal combustion engines of the type comprisingan induction pipe horizontally arranged downstream of the Venturiportion, a butterflytype throttle valve journal supported by saidinduction pipe, and an idle port on the upper wall of the induction pipebeing opened in the induction pipe adjacent the position of the topperipheral edge of the throttle valve to be assumed when the valve isclosed or slightly opened, characterized by the provision of passagemeans formed around the inner wall surface of the in-' duction pipe,said passage means functioning to prevent fuel discharged through theidle port from flowing along the upper inner wall surface of theinduction pipe in the downstream direction and conduct said flow of fueldownwardly to and above the junctures between a valve shaft forsupporting said throttle valve and the induction pipe wall, and furtherpassage means formed around the journal portions of the valve shaft,said further passage meansfunctioning to conduct said fuel flow, whichhas reached above the valve shaft, to the lower central surface area ofthe throttle valve, while turning the flow apart from the inner wall ofthe induction pipe.

2. A carburetor for internal combustion engines according to claim 1,characterized by that when the throttle valve assumes the closed orslightly opened position, said passage means provided around the innerwall surface of the induction pipe is such arranged as extending fromabove one journal portion of the valve shaft and behind the downstreamsurface of the throttle valve, to above the other journal portion of thevalve shaft, passing closely downstream of said idle port;

- while said further passage means on the valve shaft extending slightlydownstream of said surface of the throttle valve, as inclined withrespect to the shaft axis from each upper end portion of the valve shaftlocated outwardly of the inner wall surface of the induction pipe,toward the lower inner central portion of the induction pipe.

3. A carburetor for internal combustion engines according to claim 2,characterized by that said passage means provided around the inner wallsurface of the induction pipe consists of a groove formed on the innerwall surface of the induction pipe.

4. A carburetor for internal combustion engines according to claim 3,characterized by that said groove is of substantially U-shaped sectionopened inwardly of the induction pipe.

5. A carburetor for internal combustionengines according to claim 4,characterized by that said groove of U-shaped section is such'shapedover the length thereof that one side wall surface of said groove on theupstream side has a gradual increase of gradient formed from the innersurface of the induction pipe to the botthe induction pipe.

torn surface of the groove while the varying rate of said gradient beingincreased toward the lower portion of 6. A carburetor for internalcombustion engines according to claim 2, characterized by that saidpassage means provided on the inner wall surface of the induction pipeconsists of a member secured on the inner wall surface of the inductionpipe.

7. A carburetor for internal combustion engines acstream side issubstantially perpendicular to the inner wall surface of the inductionpipe.

8. A carburetor for internal combustion engines according to claim 6,characterized by that said member secured on the inner wall surface ofthe induction pipe has the outer circumferential surface substantiallyidentical to the inner circumferential surface of the induction pipe,the end surface of said member on the upstream side forming, incooperation with the inner wall surface of the induction pipe, a grooveof U- shaped section opened upstream.

9. A carburetor for internal combustion engines according to claim 2,characterized by that said passage means provided around the inner wallsurface of the induction pipe consists of a groove formed on the innerwall surface of the induction pipe and a semicylindrical member securedon the inner wall surface of the induction pipe in such a manner thatover the length of the groove, at least a half width of the opening, onthe upstream side, of the groove opened inwardly is in directcommunication with the interior of the induction pipe, the outercircumferential surface of said member being substantially identical tothe inner circumferential surface of the induction pipe.

10. A carburetor for internal combustion engines according to claim 9,characterized by that said groove is of v substantially U-shaped sectionwhile said semicylindrical member being arranged such that the endsurface of said member on the upstream side being substantiallyperpendicular to the inner wall surface of the induction pipe, and overthe length of the groove, a half width of the opening on the downstreamside being closed by said member.

11. A carburetor for internal combustion engines according to claim 9,characterized by that said groove provided around the inner wall surfaceof the induction pipe and a groove formed on the outer side of theupstream end portion of said semi-cylindrical member in combinationforms a passage generally closed such that over the upper half length,said passage is'opened in the upstream direction with a gradual increaseof the opening toward the top. of the passage.

12. A carburetor for internal combustion engines according to claim 2,characterized by that said further passage means on the-valveshaft eachextends from a portion of the inner wall surface of the induction pipe,where the outer circumferential edge of said valve shaft intersectstheinduction pipe, to the downstream surface of said throttle valve spacedinwardly from said inner wall surface of the induction pipe.

13. A carburetor for internal combustion engines according to claim 12,characterized by that said further passage means on the valve shaft eachis substantially perpendicular to the downstream surface of saidthrottle valve while said passage means each consists of a plane surfacewhich is adapted to turn upward when said throttle valve closes.

14. A carburetor for internal combustion engines according to claim 13,characterized by that said throttle valve -is supported by the valveshaft as being inserted through an axial opening provided on a portionof said valve shaft extending within the induction pipe, said axialopening having the width corresponding to the thickness of said throttlevalve and the length corresponding to the minor diameter of said valve,said portion of the valve shaft, at the downstream side of the valve,having a crosssection of trapezoid with a plane 10 surface parallel tothe downstream surface of the throttle valve, while the inner endsurface of each journal portion projecting inwardly of the inductionpipe so as to form passage means on the valve shaft.

15. A carburetor for internal combustion engines according to claim 13,characterized by that said portion of the valve shaft exposed within theinduction pipe has a semicircular section with the chord extending atthe downstream side, said throttle valve being secured on said chordcontaining surface of the valve shaft, while the inner end surface ofeach journal portion projecting inwardly of the induction pipe so as toform the passage means on the valve shaft.

' 16. A carburetor for internal combustion engines according to claim12, characterizedby that saidpassage means consists of passages ofcircular section formed through the valve shaft so that the outerextreme end of the upper opening of each passage formed on the valveshaft is positioned outwardly of the inner wall surface of the inductionpipe and the inner extreme end of said upper opening of each passage ispositioned inwardly of the'inner wall surface of the induction pipe,while the outer extreme end of the lower opening of each passage ispositioned inwardly of the inner wall surface of the induction .pipe.

17. A carburetor for internal combustion engines according to claim 2,characterized by that said throttle valve is in continuous communicationwith said further passage means on the valve shaft, while said throttlevalve being provided on the downstream surface thereof with passagemeans for conducting a flow of liquid fuel, which has been conductedonto the throttle valve by said passage means provided on the inductionpipe and valve shaft, to the downstream surface of said throttle valvespaced inwardly from the inner wall surface of the induction pipe.

18. A carburetor for internal combustion engines according to claim 17,characterized by that said passage means provided on thedownstreamsurface of the throttle valve consists of members-each having a planetop surface which continuously extends from the inner vend portion ofsaid further passage means on the valve shaft in the diagonal downwarddirection toward the lower inner central portion of the induction pipe,the inner end of each member being positioned inwardly of the outerperipheral edge of the throttle valve.

19. A carburetor for internal combustion engines according to claim 14,characterized by that said passage means provided around the inner wallsurface of the induction pipe consists of a groove having asubstantially U-shaped section opened inwardly of the induction 20. Acarburetor for internal combustion engines according to claim 16,characterized by that said passage means provided around the inner wallsurface of the induction pipe consists of agroove of substantially U-shaped section opened v inwardly of the pipe, said groove of U-shapedsection being such shaped over the length thereof that one side wallsurface of said groove on the upstream side has a gradual increase ofgradient formed from the inner wall surface of the induction pipe to thebottom surface of the groove, while the varying rate of said gradientbeing increased toward the lowerportion of the induction pipe.

21. A carburetor-for internal combustion engines according to claim 18,characterized by that said passage means provided around the inner wallsurface of the in- 1 1 duction pipe has a substantially U-shaped sectionopened'inwardly of the induction pipe, while there being provided asemi-cylindrical member having the outer circumferential surfacesubstantially identical to the inner circumferential surface of theinduction pipe, the end surface of said member on the upstream sidebeing substantially perpendicular to the inner wall surface of theinduction pipe, said member being positioned so as to substantiallyclose a half width of the groove opening, on the downstream side, overthe length of the groove.

22. A carburetor for internal combustion engines acpassage. v

1. A carburetor for internal combustion engines of the type comprisingan induction pipe horizontally arranged downstream of the Venturiportion, a butterfly-type throttle valve journal supported by saidinduction pipe, and an idle port on the upper wall of the induction pipebeing opened in the induction pipe adjacent the position of the topperipheral edge of the throttle valve to be assumed when the valve isclosed or slightly opened, characterized by the provision of passagemeans formed around the inner wall surface of the induction pipe, saidpassage means functioning to prevent fuel discharged through the idleport from flowing along the upper inner wall surface of the inductionpipe in the downstream direction and conduct said flow of fueldownwardly to and above the junctures between a valve shaft forsupporting said throttle valve and the induction pipe wall, and furtherpassage means formed around the journal portions of the valve shaft,said further passage means functioning to conduct said fuel flow, whichhas reached above the valve shaft, to the lower central surface area ofthe throttle valve, while turning the flow apart from the inner wall ofthe induction pipe.
 2. A carburetor for internal combustion enginesaccording to claim 1, characterized by that when the throttle valveassumes the closed or slightly opened position, said passage meansprovided around the inner wall surface of the induction pipe is sucharranged as extending from above one journal portion of the valve shaftand behind the downstream surface of the throttle valve, to above theother journal portion of the valve shaft, passing closely downstream ofsaid idle port; while said further passage means on the valve shaftextending slightly downstream of said surface of the throttle valve, asinclined with respect to the shaft axis from each upper end portion ofthe valve shaft located outwardly of the inner wall surface of theinduction pipe, toward the lower inner central portion of the inductionpipe.
 3. A carburetor for internal combustion engines according to claim2, characterized by that said passage means provided around the innerwall surface of the induction pipe consists of a groove formed on theinner wall surface of the induction pipe.
 4. A carburetor for internalcombustion engines according to claim 3, characterized by that saidgroove is of substantially U-shaped section opened inwardly of theinduction pipe.
 5. A carburetor for internal combustion enginesaccording to claim 4, characterized by that said groove of U-shapedsection is such shaped over the length thereof that one side wallsurface of said groove on the upstream side has a gradual increase ofgradient formed from the inner surface of the induction pipe to thebottom surface of the groove while the varying rate of said gradientbeing increased toward the lower portion of the induction pipe.
 6. Acarburetor for internal combustion engines according to claim 2,characterized by that said passage means provided on the innEr wallsurface of the induction pipe consists of a member secured on the innerwall surface of the induction pipe.
 7. A carburetor for internalcombustion engines according to claim 6, characterized by that saidmember secured on the inner wall surface of the induction pipe is in theform of a semi-cylindrical member which has the outer circumferentialsurface substantially identical to the inner circumferential surface ofthe induction pipe, and the end surface of said member on the upstreamside is substantially perpendicular to the inner wall surface of theinduction pipe.
 8. A carburetor for internal combustion enginesaccording to claim 6, characterized by that said member secured on theinner wall surface of the induction pipe has the outer circumferentialsurface substantially identical to the inner circumferential surface ofthe induction pipe, the end surface of said member on the upstream sideforming, in cooperation with the inner wall surface of the inductionpipe, a groove of U-shaped section opened upstream.
 9. A carburetor forinternal combustion engines according to claim 2, characterized by thatsaid passage means provided around the inner wall surface of theinduction pipe consists of a groove formed on the inner wall surface ofthe induction pipe and a semi-cylindrical member secured on the innerwall surface of the induction pipe in such a manner that over the lengthof the groove, at least a half width of the opening, on the upstreamside, of the groove opened inwardly is in direct communication with theinterior of the induction pipe, the outer circumferential surface ofsaid member being substantially identical to the inner circumferentialsurface of the induction pipe.
 10. A carburetor for internal combustionengines according to claim 9, characterized by that said groove is ofsubstantially U-shaped section while said semi-cylindrical member beingarranged such that the end surface of said member on the upstream sidebeing substantially perpendicular to the inner wall surface of theinduction pipe, and over the length of the groove, a half width of theopening on the downstream side being closed by said member.
 11. Acarburetor for internal combustion engines according to claim 9,characterized by that said groove provided around the inner wall surfaceof the induction pipe and a groove formed on the outer side of theupstream end portion of said semi-cylindrical member in combinationforms a passage generally closed such that over the upper half length,said passage is opened in the upstream direction with a gradual increaseof the opening toward the top of the passage.
 12. A carburetor forinternal combustion engines according to claim 2, characterized by thatsaid further passage means on the valve shaft each extends from aportion of the inner wall surface of the induction pipe, where the outercircumferential edge of said valve shaft intersects the induction pipe,to the downstream surface of said throttle valve spaced inwardly fromsaid inner wall surface of the induction pipe.
 13. A carburetor forinternal combustion engines according to claim 12, characterized by thatsaid further passage means on the valve shaft each is substantiallyperpendicular to the downstream surface of said throttle valve whilesaid passage means each consists of a plane surface which is adapted toturn upward when said throttle valve closes.
 14. A carburetor forinternal combustion engines according to claim 13, characterized by thatsaid throttle valve is supported by the valve shaft as being insertedthrough an axial opening provided on a portion of said valve shaftextending within the induction pipe, said axial opening having the widthcorresponding to the thickness of said throttle valve and the lengthcorresponding to the minor diameter of said valve, said portion of thevalve shaft, at the downstream side of the valve, having a cross sectionof trapezoid with a plane surface parallel to the downstream surface ofthe throttle valve, while the inner end surface of each journal portionprojecting inwardly of the induction pipe so as to form passage means onthe valve shaft.
 15. A carburetor for internal combustion enginesaccording to claim 13, characterized by that said portion of the valveshaft exposed within the induction pipe has a semicircular section withthe chord extending at the downstream side, said throttle valve beingsecured on said chord containing surface of the valve shaft, while theinner end surface of each journal portion projecting inwardly of theinduction pipe so as to form the passage means on the valve shaft.
 16. Acarburetor for internal combustion engines according to claim 12,characterized by that said passage means consists of passages ofcircular section formed through the valve shaft so that the outerextreme end of the upper opening of each passage formed on the valveshaft is positioned outwardly of the inner wall surface of the inductionpipe and the inner extreme end of said upper opening of each passage ispositioned inwardly of the inner wall surface of the induction pipe,while the outer extreme end of the lower opening of each passage ispositioned inwardly of the inner wall surface of the induction pipe. 17.A carburetor for internal combustion engines according to claim 2,characterized by that said throttle valve is in continuous communicationwith said further passage means on the valve shaft, while said throttlevalve being provided on the downstream surface thereof with passagemeans for conducting a flow of liquid fuel, which has been conductedonto the throttle valve by said passage means provided on the inductionpipe and valve shaft, to the downstream surface of said throttle valvespaced inwardly from the inner wall surface of the induction pipe.
 18. Acarburetor for internal combustion engines according to claim 17,characterized by that said passage means provided on the downstreamsurface of the throttle valve consists of members each having a planetop surface which continuously extends from the inner end portion ofsaid further passage means on the valve shaft in the diagonal downwarddirection toward the lower inner central portion of the induction pipe,the inner end of each member being positioned inwardly of the outerperipheral edge of the throttle valve.
 19. A carburetor for internalcombustion engines according to claim 14, characterized by that saidpassage means provided around the inner wall surface of the inductionpipe consists of a groove having a substantially U-shaped section openedinwardly of the induction pipe.
 20. A carburetor for internal combustionengines according to claim 16, characterized by that said passage meansprovided around the inner wall surface of the induction pipe consists ofa groove of substantially U-shaped section opened inwardly of the pipe,said groove of U-shaped section being such shaped over the lengththereof that one side wall surface of said groove on the upstream sidehas a gradual increase of gradient formed from the inner wall surface ofthe induction pipe to the bottom surface of the groove, while thevarying rate of said gradient being increased toward the lower portionof the induction pipe.
 21. A carburetor for internal combustion enginesaccording to claim 18, characterized by that said passage means providedaround the inner wall surface of the induction pipe has a substantiallyU-shaped section opened inwardly of the induction pipe, while therebeing provided a semi-cylindrical member having the outercircumferential surface substantially identical to the innercircumferential surface of the induction pipe, the end surface of saidmember on the upstream side being substantially perpendicular to theinner wall surface of the induction pipe, said member being positionedso as to substantially close a half width of the groove opening, on thedownstream side, over the length of the groove.
 22. A carburetor forinternal combustion engines according to claim 15, charActerized by thatsaid passage means provided around the inner wall surface of theinduction pipe consists of a groove formed on the inner wall surface ofthe induction pipe and a further groove formed on the outer side of theupstream end portion of a semi-cylindrical member secured on the innerwall surface of the induction pipe, thereby forming a generally closedpassage such that over the upper half length, said passage is opened inthe upstream direction with a gradual increase of the opening toward thetop of the passage.